Thescienceofobsession asked for meta. Spoilers.
The big deal here is that Mary is equating them, Science. Her statement groups Sherlock’s relationship with John together with Mary’s relationship with John. She is likening them in both intensity and, at least to some extent, in type.
It also says something about the way John does relationships. We know that, to other people, John talks about Sherlock incessantly. I mean, just check out the blog. And now we know that to Mary, who already knows Sherlock, he talks endlessly about Major Shalto in much the same way. (And apparently before Sherlock came back, he talked endlessly about Sherlock, because Mary knew the significance of Sherlock frolicking back into John’s life.)
I don’t know what it means that John never talked to Sherlock about Major Shalto. Maybe that’s something like going on to the person you’re dating about your ex? *shrug*
